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Original Investigation
April 23/30, 2019

Association of State Medicaid Expansion Status With Low Birth Weight and Preterm Birth

Author Affiliations
  • 1Department of Health Policy and Management, University of Arkansas for Medical Sciences, Little Rock
  • 2Institute for Medicaid Innovation, Washington, DC
  • 3Department of Obstetrics and Gynecology, University of Michigan Medical School, Ann Arbor
  • 4Department of Obstetrics and Gynecology, University of Arkansas for Medical Sciences, Little Rock
JAMA. 2019;321(16):1598-1609. doi:10.1001/jama.2019.3678
Key Points

Question  Was state Medicaid expansion associated with differences in rates of low birth weight and preterm birth, both overall and in terms of racial/ethnic disparities?

Findings  In this observational study of 15 631 174 births from 2011 to 2016, state Medicaid expansion was not significantly associated with differences in rates of low birth weight or preterm birth outcomes overall. There were significant reductions in relative disparities for black infants (preterm birth: −0.43 percentage points, very preterm birth: −0.14 percentage points, low birth weight: −0.53 percentage points, and very low birth weight: −0.13 percentage points) but not for Hispanic infants relative to white infants in states that expanded Medicaid compared with those that did not.

Meaning  State Medicaid expansion was not associated with differences in rates of low birth weight or preterm birth outcomes overall, but was associated with improvements in relative disparities for black infants compared with white infants among the states that expanded compared with those that did not.

Abstract

Importance  Low birth weight and preterm birth are associated with adverse consequences including increased risk of infant mortality and chronic health conditions. Black infants are more likely than white infants to be born prematurely, which has been associated with disparities in infant mortality and other chronic conditions.

Objective  To evaluate whether Medicaid expansion was associated with changes in rates of low birth weight and preterm birth outcomes, both overall and by race/ethnicity.

Design, Setting, and Participants  Using US population-based data from the National Center for Health Statistics Birth Data Files (2011-2016), difference-in-differences (DID) and difference-in-difference-in-differences (DDD) models were estimated using multivariable linear probability regressions to compare birth outcomes among infants in Medicaid expansion states relative to non–Medicaid expansion states and changes in relative disparities among racial/ethnic minorities for singleton live births to women aged 19 years and older.

Exposures  State Medicaid expansion status and racial/ethnic category.

Main Outcomes and Measures  Preterm birth (<37 weeks’ gestation), very preterm birth (<32 weeks’ gestation), low birth weight (<2500 g), and very low birth weight (<1500 g).

Results  The final sample of 15 631 174 births (white infants: 8 244 924, black infants: 2 201 658, and Hispanic infants: 3 944 665) came from the District of Columbia and 18 states that expanded Medicaid (n = 8 530 751) and 17 states that did not (n = 7 100 423). In the DID analyses, there were no significant changes in preterm birth in expansion relative to nonexpansion states (preexpansion to postexpansion period, 6.80% to 6.67% [difference: −0.12] vs 7.86% to 7.78% [difference: −0.08]; adjusted DID: 0.00 percentage points [95% CI, −0.14 to 0.15], P = .98), very preterm birth (0.87% to 0.83% [difference: −0.04] vs 1.02% to 1.03% [difference: 0.01]; adjusted DID: −0.02 percentage points [95% CI, −0.05 to 0.02], P = .37), low birth weight (5.41% to 5.36% [difference: −0.05] vs 6.06% to 6.18% [difference: 0.11]; adjusted DID: −0.08 percentage points [95% CI, −0.20 to 0.04], P = .20), or very low birth weight (0.76% to 0.72% [difference: −0.03] vs 0.88% to 0.90% [difference: 0.02]; adjusted DID: −0.03 percentage points [95% CI, −0.06 to 0.01], P = .14). Disparities for black infants relative to white infants in Medicaid expansion states compared with nonexpansion states declined for all 4 outcomes, indicated by a negative DDD coefficient for preterm birth (−0.43 percentage points [95% CI, −0.84 to −0.02], P = .05), very preterm birth (−0.14 percentage points [95% CI, −0.26 to −0.02], P = .03), low birth weight (−0.53 percentage points [95% CI, −0.96 to −0.10], P = .02), and very low birth weight (−0.13 percentage points [95% CI, −0.25 to −0.01], P = .04). There were no changes in relative disparities for Hispanic infants.

Conclusions and Relevance  Based on data from 2011-2016, state Medicaid expansion was not significantly associated with differences in rates of low birth weight or preterm birth outcomes overall, although there were significant improvements in relative disparities for black infants compared with white infants in states that expanded Medicaid vs those that did not.

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